The quick heating and cooling of the batts in kilns in the ceramic industry gives rise to considerable internal stresses. It is known to reduce the stresses upon heating by providing slot-like recesses in those batts. These slots start at the side edges and are directed inwardly and may be as long as one fourth of the width of the batt. Often such marginial slots extend from about 150 to 200 mm in parallel with the narrow sides of the batt. Experience has shown that this measure does relieve the stresses which occur upon heating, but is no sufficienty remedy in the cooling process.